This application relates generally to gas turbine engine rotor blades and, more particularly, to methods and apparatus for reducing rotor blade tip temperatures.
Gas turbine engine rotor blades typically include airfoils having leading and trailing edges, a pressure side, and a suction side. The pressure and suction sides connect at the airfoil leading and trailing edges, and span radially between the airfoil root and the tip. To facilitate reducing combustion gas leakage between the airfoil tips and stationary stator components, the airfoils include a tip region that extends radially outward from the airfoil tip.
The airfoil tip regions include a first tip wall extending from the airfoil leading edge to the trailing edge, and a second tip wall also extending from the airfoil leading edge to connect with the first tip wall at the airfoil trailing edge. The tip region prevents damage to the airfoil if the rotor blade rubs against the stator components.
During operation, combustion gases impacting the rotating rotor blades transfer heat into the blade airfoils and tip regions. Over time, continued operation in higher temperatures may cause the airfoil tip regions to thermally fatigue. To facilitate reducing operating temperatures of the airfoil tip regions, at least some known rotor blades include slots within the tip walls to permit combustion gases at a lower temperature to flow through the tip regions.
To facilitate minimizing thermal fatigue to the rotor blade tips, at least some known rotor blades include a shelf adjacent the tip region to facilitate reducing operating temperatures of the tip regions. The shelf is defined to extend partially within the pressure side of the airfoil to disrupt combustion gas flow as the rotor blades rotate, thus enabling a film layer of cooling air to form against a portion of the pressure side of the airfoil.
In an exemplary embodiment, a rotor blade for a gas turbine engine includes a tip region that facilitates reducing operating temperatures of the rotor blade, without sacrificing aerodynamic efficiency of the turbine engine. The tip region includes a first tip wall and a second tip wall that extend radially outward from an airfoil tip plate. The first tip wall extends from a leading edge of the airfoil to a trailing edge of the airfoil. The second tip wall also extends from the airfoil leading edge and connects with the first tip wall at the airfoil trailing edge to define an open-top tip cavity. At least a portion of the second tip wall is recessed to define a tip shelf that extends between the airfoil leading and trailing edges.
During operation, as the rotor blades rotate, combustion gases at a higher temperature near a pitch line of each rotor blade migrate to the airfoil tip region and towards the rotor blade trailing edge. Because the tip walls extend from the airfoil, a tight clearance is defined between the rotor blade and stationary structural components that facilitates reducing combustion gas leakage therethrough. If rubbing occurs between the stationary structural components and the rotor blades, the tip walls contact the stationary components and the airfoil remains intact. As the rotor blade rotates, combustion gases at lower temperatures near the leading edge of the tip region flow past the airfoil tip shelf. The tip shelf disrupts the combustion gas radial flow causing the combustion gases to separate from the airfoil sidewall, thus facilitating a decrease in heat transfer thereof. As a result, the tip shelf facilitates reducing operating temperatures of the rotor blade within the tip region, but without consuming additional cooling air, thus improving turbine efficiency.